Mobile computing and communication devices are becoming extremely prevalent, and there is great interest in providing location specific services and information to the users of mobile devices. Mobile devices such as smart phones, media players, and personal digital assistants (PDA) often include Global Positioning Satellite (GPS) systems for identifying the device's location. The positions of cellular devices may also be determined using triangulation from cell phone towers. Typically, these systems are used to determine the positions of mobile devices to accuracies on the order of tens or hundreds of meters. These levels of accuracy may not be sufficient for some purposes, and systems such as GPS may not function indoors.